Electrical switching incorporating controllable bistable characteristics



s. B. ALLEN 3,233,068 ELECTRICAL SWITCHING INCORPORATING CONTROLLABLE Feb. 1, 1966 BISTABLE CHARACTERISTICS Filed May 17, 1965 INVENTOR.

STRATFORD B. ALLEN BY I ATTORNEYS United States Patent I 3,233,068 ELECTRICAL SWITCHING INCORPORATING CON- TROLLABLE BISTABLE CHARACTERISTICS Stratford B. Allen, Sharon, Mass, assignor to Joseph Pollak Corporation, Dorchester, Mass, a corporation of Massachusetts Filed May 17, 1963, Ser. No. 281,272 7 Claims. (Cl. 200122) The present invention relates in general to electrical switching and more particularly concerns electrical switching apparatus responsive to changes in temperature for selectively controlling the transfer of electrical energy. The switching apparatus according to the invention is capable of exhibiting bistable characteristics relatively easy to control through both electrical and mechanical means. Yet the structure is relatively compact and relatively easy to fabricate on a production basis.

An art structure comprises a pair of bimetallic elements fastened together at one end with, and separated by, one end of each of three flexible strips. The intermediate strip functions as a switch blade and carries a contact at its other end. The other end of each of the other strips is fastened to a respective strip support means to which is also fastened the other end of a respective bimetallic element. Each bimetallic element is formed with a U-shaped port-ion intermediate its ends for accommodating a heating resistor. While that prior invention performs well, it does not have as much flexibility of control as would be desired. Moreover, thermal transfer efiiciency between the heating resistor and the bimetallic element is not as great as would be desired.

Accordingly, it is an important object of the present invention to improve the prior invention by providing means for controlling the switching characteristics of the device and improving the efficiency of thermal transfer between heating element and bimetallic strips.

According to an important aspect of the invention, a bimetallic upwardly opening U-shaped bimetallic element has the end of one leg secured to a supporting base while the other leg is free to move relative to that supporting base in response to heat transferred from a heating ele ment surrounded by the bight of the U-shaped bimetallic element.

In a representative embodiment of the invention, the first and second of these generally U-shaped bimetallic elements are arranged side by side with each having an outside leg separated from the outside leg of the other by the two inside legs. Support means maintain the outside legs in fixed relationship while allowing relative movement between each inside leg and each outside leg. Means interconnecting the inside legs move relative to the support means in responsive to movement of the inside legs interconnected thereby. A slightly bowed switch blade may be connected at one end to the interconnecting means and have a contact at its other end. Means may support that switch blade so that its contact moves from one stable position to another in response to movement of the interconnecting means from one stable position to another, the latter means for supporting, the outside legs support means, the interconnecting means and the bimetallic elements coacting to establish the two stable positions.

First and second sources of heat may be located inside and adjacent to the respective bights of the first and second U-shaped bimetallic elements. Typically these sources may be resistive elements each having first and second leads. First and second insulatedly separated opposed contacts may be arranged to be separated by the switch blade contact and connected to respective first leads of the first and second resistive elements. Means ice may be provided for supporting the resistive element second leads in fixed relationship with respect to the outside legs support means. Means may also support the first and second contacts in fixed relationship with respect to the latter support means and positioned so that the switch blade contact contacts respective ones of the first and second contacts when the switch blade is in respective ones of its stable positions.

A feature of the switch blade supporting means in a specific embodiment of the invention resides in providing first and second triplets of generally parallel resilient strips on opposite sides of the switch blade and fastened together at one end of each strip by means for maintaining the fastened together ends in fixed relationship with respect to the interconnecting means. The first and second triplet support means on opposite sides of the switch blade in fixed relationship with respect to the outside legs support means maintains the other ends of each outside pair of first and second triplets respectively in fixed realtionship with respect to the outside leg support means and maintain the outside pairs bowed in toward the switch blade. First and second adjutsing means carried by the first and second triplet support means respectively control the spacing between the respective triplet support means and another end of a respective intermediate strip of the triplets to control the switching characteristics of the apparatus.

Numerous other features, objects and advantages of the invention will become apparent from the following specification when read in conjunction with the accompanying drawing in which:

FIG. 1 is an exploded view of an exemplary embodiment of the invention;

FIG. 2 is a front view of the assembled embodiment; and

FIG. 3 is a schematic electromechanical circuit diagram of the invention used in a circuit for alternatively flashing a pair of lights.

With reference now to the drawing and more particularly FIGS. 1 and 2 thereof, there is illustrated an exemplary embodiment of the invention, FIG. 1 showing an exploded perspective view of the embodiment and FIG. 2 showing a front view of the assembled embodiment. A base 11 of Bakelite or other suitable material, preferably insulating, is oriented normally with its length along the vertical direction as shown. Base 11 supports a generally U-shaped bracket 12 which is riveted to the top recessed edge shelf 13 of base 11 with its left leg 14 and right leg 15 normally horizontally aligned.

Generally U-shaped left bimetallic element 16 has its outside leg 17 secured to left leg 14 of bracket 12, typically by means of clamping plate 19 and screws 18 residing in tapped openings in left leg 14. Generally U-shaped bimetallic element 21 has its outside leg 22 secured to right leg 15 of bracket 12 by means of clamping plate 20 and screws 23 secured in tapped openings in right leg 15.

A switch blade assembly comprises an axially bifurcated flexible conducting strip 24 carrying a contact assembly at its bottom and comprising a bifurcated contact support base 25 riveted thereto and carrying the left and right contacts 26 and 27 welded to opposite sides of support base 25.

The bifurcated switch blade 24 separates a left triplet of generally parallel resilient strips comprising an outside pair 32 and an intermediate strip 33 from a right triplet of generally parallel resilient strips comprising an outside pair 34 and an intermediate strip 35. Th top ends of the left and right triplets and the closed end of the bifurcated contact blade 24 are held together tightly between a left clamping plate 36 and right clamping plate 37 all riveted together. Left clamping plate 36 and right clamping plate 37 are formed with edges 38 and 39, respectively, extending upwardly and away from the riveted together top ends.

A central rivet 41 interconnects the inside leg 42 of left bimetallic element 16 and the inside leg 43 of right bimetallic element 21 while the edge 38 bears against the inside leg 42 and the edge 39 bears against the inside leg 43 with rivet 41 passing through the bights in the riveted together clamping plates 36 and 37 and switch blade 24 so that these clamped together edges 38 and 39 follow the movement of inside legs 42 and 43 held spaced by rivet 41 as they move together in response to temperature changes.

A lower bracket 44 is formed with an arcuate backplate 45 having a generally horizontal tab 46, arcuate backplate 45 residing in the mating arcuate groove 47 in base 11 while tab 46 passes through slot 47' to form a terminal at the rear of base plate 11 to establish electrical connection with the switch blade contacts 26 and 27.

A left clamping plate 51 clamps the lower ends of left outside pair 32 to the inside face of left sloping leg 52 of bracket 44. Right clamping plate 53 clamps the lower ends of right outside pair 34 to the inside face of right sloping leg 54 of lower bracket 44, the latter clamping plates being riveted to the latter sloping legs.

A left adjusting screw 55 presses against the lower portion of intermediate strip 33 to fix the distance between that strip and left sloping leg 52 and thereby control the force exerted upon the switch blade strips 24 from the left. Right set screw 56 permits adjustment of the separation between the lower portion of right intermediate strip 35 and right sloping leg 54 to control the spring force exerted upon the switch blade from the right.

A left contact supporting bracket 57 carries a left contact 58 and is supported in the vertical groove 61 in base plate 11. Its back plate 62 is riveted to the back of base 11 and rests in the groove 63 with rearwardly extending tab 60 available for electrical connection to contact 58. Similarly right fixed contact support bracket 64 resides in slot 65 of base 11 and supports right fixed contact 66. Its back plate 67 is riveted to the back of base plate 11 and resides in the groove (not shown) similar to groove 63 with the rearwardly extending tab 68 available for electrical connection to fixed contact 66.

A plate of insulating material 71 is formed with slots 72 and 73 that accommodate front tabs 74 and 75 respectively of left fixed contact support 57 and right fixed contact support 64. Plate 71 is held in place by solder connection of resistor terminal wires 82 and 86 to tabs 74 and 75, respectively.

A heating resistor 76 is surrounded by the bight portion 77 of the left bimetallic element 16 and has its rear lead 78 passing through opening 81 in base 11 Where it may be connected to an external circuit. Its front lead 82 is bent at a right angle to the body of left re sistor 76 and soldered to front tab 74 of left fixed contact bracket 57. Right resistor 83 is surrounded by the bight 84 of right bimetallic element 21 and has its rear lead 85 passing through opening 86 in base plate 11. Its front lead 86 is bent at right angles to its body and soldered to tab 75 of right fixed contact support 64.

Switch blade 24 is bowed slightly to the left as shown when in one of its stable positions with right switch blade contact 27 contacting right fixed contact 66. In the other of its stable positions with left switch blade contact 27 in contact with left fixed contact 58, switch blade 24 is bowed to the right. The left outside pair 32 and the right outside pair 34 are bowed toward the blade 24.

According to a preferred form of the invention, the bifurcated support base 25 coacts with the plate 29 to maintain the legs of bifurcated switch blade 24 toed in sufficiently to establish a desired contact pressure, typically of the order of 25 grams. To this end support base 25 is formed of relatively soft material, such as soft brass, and plate 29 is formed of relatively hard material, such as hard brass. Plate 29 is also formed with a slotted rivet opening 40 near the adjacent flat edge 30 to permit adjustment of the spacing between the legs of blade 24. This adjustment is preferably done while maintaining the ends of the two legs of blade 24 fiat. With the rivets holding the ends of the legs of blade 24 sandwiched between bifurcated support base 25 and plate 29 loose enough to permit sliding movement between plate 29 and the leg of blade 24 adjacent to slottted opening 40, the legs of bifurcated support base 25 may be urged together until the desired spacing is obtained to stress blade 24 inside its elastic limit, typically when the edge of the last-mentioned leg of blade 24 is substantially flush with the fiat edge 36. The rivets are then flattened to maintain this alignment. The relatively soft brass base 25 yields to conform to this aligned position in being stressed beyond its elastic limit While the hard brass plate 29 keeps the ends of the legs of blade 24 essentially coplanar. It has been discovered that slight adjustments of the leg spacing may be made in the assembled switching assembly to establish precise control over individual units, especially if the rivets are not flattened excessively during initial assembly.

Still another modification helpful in distributing the stresses more uniformly over switch blade 24 resides in placing a small washer on either side of the C-shaped opening between the blades held together by a rivet passing through this opening to apply forces tending to flatten the dome about this opening. The diameter of this washer is greater than the diameter of this C-shaped opening. This insertion is also preferably done after toeing in the legs of blade 24.

If set screw 55 is rotated clockwise, the force exerted on switch contact blade 24 by the left triplet tending to move it to the other of its stable positions is increased and less additional force is required to effect switching. By rotating set screw 56 clockwise, the force exerted by the right triplet tending to keep switch blade 24 in the stable position shown is increased and more additional force is required to switch the blade 24 to the other of its stable positions. In the position shown, the set screw 55 exerts considerably more control over the force required to switch contact blade 24 to its other stable position than set screw 56 While the converse is true when switch blade 24 is in the other of its stable positions. Thus, set screws 55 and 56 provide essentially independent control over the amount of force required to switch the switch blade 24 from one stable position to the other. This arrangement effectively provides mechanical control over the duration of a switching cycle as will be better understood from the discussion of the principles of operation described below.

Having now discussed the structure of an embodiment of the invention, it is appropriate to consider the principles of operation. Understanding the principles of operation will be better understood by considering an exemplary system in which the invention may be used to form alternately flashing lamps 91 and 92 shown in FIG. 3 by switching the power from source 93 from one lamp to the other alternately. Consider the situation in which contact blade 24 has just assumed the position shown to short out right resistor 83 and thereby extinguish bulb 91 connected in parallel therewith while removing the short circuit across resistor 76 and thereby igniting bulb 92 connected across that resistor. Right resistor 83 begins to cool, causing bimetallic element 21 to contract and inside leg 43 to move to the left. At the same time left resistor 76 heats up, causing bimetallic element 16 to expand and inside leg 42 also to move to the left so that rivet 41 and the connected together ends between clamping plates 36 and 37 all move to the left and switch blade 24 flips to its other stable position with left contact 26 in contact with left fixed contact 58 with blade 24 bowed to the right, thereby short circuiting resistor 76 and ex 'tinguishing bulb 92 while allowing resistor 83 to again heat and igniting bulb 91 until contraction of bimetallic element 16 and expansion of bimetallic element 21 moves rivet 41 to the right to complete a switching cycle. The length of each cycle may be controlled by adjusting the set screws 55 and 56 mechanically or by connecting variable shunt resistances across the resistors. The duration of a switching period may be controlled by controlling the potential delivered by power source 93. The invention thus provides a great deal of control over its switching characteristics.

Numerous other uses, modifications of and departures from the specific embodiment described herein will become apparent to those skilled in the art without departing from the inventive concepts. Consequently, the invention is to be construed as limited solely by the spirit and scope of the intended claims.

What is claimed is:

1. Electrical switching apparatus comprising,

first and second generally U-shaped bimetallic elements arranged side by side each having an outside leg separated from the outside leg of the other by the two inside legs,

support means for maintaining said outside legs in fixed relationship while allowing relative movement between each inside leg and each outside leg, and means interconnecting said inside legs for movement relative to said support means in response to movement of said inside legs interconnected thereby,

a slightly bowed switch blade connected at one end to said interconnecting means and having a contact at its other end,

means for supporting said switch blade so that said contact moves from one stable position to another in response to movement of said interconnecting means from one stable position to another,

the latter means for supporting, said support means,

said interconnecting means, and said bimetallic elements coacting to establish said two stable positions, said means for supporting said switch blade comprising, first and second triplets of generally parallel resilient strips on opposite side-s of said switch blade and fastened together at one end of each strip by means for maintaining the fastened together ends in fixed relationship with said interconnecting means,

first and second triplet support means on opposite sides of said switch blade in fixed relationship with respect to said support means for maintaining the other ends of each outside pair of said first and second triplets respectively in fixed relationship with respect to said support means and maintaining said outside pairs bowed in toward said switch blade,

and first and second adjusting means carried by said first and second triplet support means respectively for controlling the spacing between a respective triplet support means and another end of a respective intermediate strip of said triplets.

2. Electrical switching apparatus in accordance with claim 1 and further comprising,

first and second sources of heat respectively located inside and adjacent to the respective bights of said first and second U-shaped bimetallic elements,

said first and second sources comprising electrical resistive elements each having first and second leads, said electrical switching apparatus further comprising, first and second insulatedly separated opposed contacts separated by said switch blade contact and connected to respective first leads of said first and second resistive elements of said first and second resistive elements,

means for supporting said resistive element second leads in fixed relationship with respect to said support means,

and means for supporting said first and second contacts in fixed relationship with respect to said support means and positioned so that said switch blade contact contacts said first and second contacts when said switch blade is in respective ones of its stable position.

3. For use in electrical switching, an apparatus comprising a bifurcated switch blade resilient element having first and second legs,

a bifurcated contact support base of yieldable material having first and second legs whose spacing may be changed to a new spacing by applying suflicient relative force between the latter legs which new spacing is retained upon removal of said sufficient relative force,

a flat plate of hard material much less yieldable than said support base material,

and means for clamping the ends of said contact base legs between the ends of respective ones of said support base legs and said flat plate to maintain a prescribed toe-in between said contact legs and stress said blade element inside its elastic limit while keeping the ends of the latter contact legs flat in the same plane.

4. Apparatus in accordance with claim 3 wherein said clamping means comprise rivets,

said plate is formed with a slotted opening near a flat end thereof to permit at least one of said rivets to move along the length of said slot while the latter rivet remains stationary with respect to one of said contact legs to permit alignment of an outside edge of said one contact leg with said plate fiat end.

5. Apparatus in accordance with claim 3 wherein said bifurcated switch blade is formed with a domed portion joining the first and second legs,

and means for applying pressure to said domed portion tending to urge said first and second legs apart.

6. Apparatus in accordance with claim 4 wherein said bifurcated switch blade is formed with a domed portion joining the first and second legs,

and means for applying pressure to said domed portion tending to urge said first and second legs apart.

7. Apparatus in accordance with claim '6 wherein said means for applying pressure comprises washers adjacent to said domed portion clamped between said first and second legs.

References Cited by the Examiner UNITED STATES PATENTS 2,335,212 11/1943 Landon 200122 2,446,831 8/1948 Hottenroth 200-122 2,592,952 4/1952 Ray 200-422 2,758,175 8/1956 Hotchkiss 200-122 2,769,938 11/1956 Pauly 2OO-122 FOREIGN PATENTS 18,382 7/1934 Australia.

0 BERNARD A. GILHEANY, Primary Examiner. 

1. ELECTRICAL SWITCHING APPARATUS COMPRISING, FIRST AND SECOND GENERALLY U-SHAPED BIMETALLIC ELEMENTS ARRANGED SIDE BY SIDE EACH HAVING AN OUTSIDE LEG SEPARATED FROM THE OUTSIDE LEG OF THE OTHER BY THE TWO INSIDE LEGS, SUPPORT MEANS FOR MAINTAINING SAID OUTSIDE LEGS IN FIXED RELATIONSHIP WHILE ALLOWING RELATIVE MOVEMENT BETWEEN EACH INSIDE LEG AND EACH OUTSIDE LEG, AND MEANS INTERCONNECTING SAID INSIDE LEGS FOR MOVEMENT RELATIVE TO SAID SUPPORT MEANS IN RESPONSE TO MOVEMENT OF SAID INSIDE LEGS INTERCONNECTED THEREBY, A SLIGHTLY BOWED SWITCH BLADE CONNECTED AT ONE END TO SAID INTERCONNECTING MEANS AND HAVING A CONTACT AT ITS OTHER END, MEANS FOR SUPPORTNG SAID SWITCH BLADE SO THAT SAID CONTACT MOVES FROM ONE STABLE POSITION TO ANOTHER IN RESPONSE TO MOVEMENT OF SAID INTERCONNECTING MEANS FROM ONE STABLE POSITION TO ANOTHER, THE LATTER MEANS FOR SUPPORTING, SAID SUPPORT MEANS, SAID INTERCONNECTING MEANS, AND SAID BIMETALLIC ELEMENTS COACTING TO ESTABLISH SAID TWO STATE POSITIONS, SAID MEANS FOR SUPPORTING SAID SWITCH BLADE COMPRISING, FIRST AND SECOND TRIPLETS OF GENERALLY PARALLEL RESILIENT STRIPS ON OPPOSITE SIDES OF SAID SWITCH BLADE AND FASTENED TOGETHER AT ONE END OF EACH STRIP BY MEANS FOR MAINTAINING THE FASTENED TOGETHER ENDS IN FIXED RELATIONSHIP WITH SAID INTERCONNECTING MEANS, FIRST AND SECOND TRIPLET SUPPORT MEANS ON OPPOSITE SIDES OF SAID SWITCH BLADE IN FIXED RELATIONSHIP WITH RESPECT TO SAID SUPPORT MEANS FOR MAINTAINING THE OTHER ENDS OF EACH OUTSIDE PAIR OF SAID FIRST AND SECOND TRIPLETS RESPECTIVELY IN FIXED RELATIONSHIP WITH RESPECT TO SAID SUPPORT MEANS AND MAINTAINING SAID OUTSIDE PAIRS BOWED IN TOWARD SAID SWITCH BLADE, AND FIRST AND SECOND ADJUSTING MEANS CARRIED BY SAID FIRST AND SECOND TRIPLET SUPPORT MEANS RESPECTIVELY FOR CONTROLLING THE SPACING BETWEEN A RESPECTIVE TRIPLET SUPPORT MEANS AND ANOTHER END OF A RESPECTIVE INTERMEDIATE STRIP OF SAID TRIPLETS. 